Our studies focus on the relationship between the regulation of amino acid biosynthesis and the regulation of cell division. We have mutants (tra) which are simultaneously defective in cell division and in the regulation of amino acid biosynthesis. Genetic and biochemical techniques will be used to elucidate the mechanism of TRA gene control. How does the TRA gene product regulate structural genes of amino acid biosynthesis and at the same time cell division? To answer this question we will: 1) Isolate mutations in the regulatory elements next to the his4 structural gene. 2) Map and define this regulatory gene by deletion analysis. 3) See how the adjacent regulatory gene interacts with the alleles of the TRA gene. 4) See if the potential for derepression is restricted to a portion of the cell cycle. 5) Test for the possibility of a his complex in the cell. 6) Try to develop a system for in vitro synthesis of his4 proteins. Several selection schemes designed to answer these questions are new and, if successful, could have utility in a number of genetic systems. All of our work is done on the yeast Saccharomyces cerevisiae.